This invention relates generally to pressure sensors and more particularly to apparatus for housing pressure responsive, variable, parallel plate capacitive transducers having, in plan view, a rectangular configuration and associated conditioning electronics.
Sensors comprising pressure responsive, variable, parallel plate capacitive transducers having a generally circular disc shaped configuration are well known. An example of such sensors is shown and described in U.S. Pat. No. 4,716,492, assigned to the assignee of the present invention. In that patent a capacitive transducer is shown having a thin, generally cylindrical ceramic diaphragm mounted in closely spaced, sealed, overlying relation to a generally cylindrical ceramic base with metal layers on respective facing surfaces of the diaphragm and base to serve as capacitor plates arranged in predetermined closely spaced relation to each other to form a capacitor. Transducer terminals connected to the capacitor plates are arranged at an opposite surface of the transducer base and a signal conditioning electrical circuit, connected to the transducer terminals, is mounted on the transducer. A cup-shaped connector body of electrical insulating material is fitted over the electrical circuit and is secured to the transducer by a port fitting which has a port for exposing the transducer diaphragm to an applied fluid pressure. The diaphragm is movable in response to variations in fluid pressure applied to the diaphragm to vary the capacitance of the capacitor in accordance with the changes in applied pressure and the electrical circuit provides an electrical output signal corresponding to the applied pressure.
In copending U.S. Pat. No. 5,880,371, rectangular (in plan view) pressure sensing capacitive transducer elements are disclosed and claimed. The present invention relates to apparatus for housing such rectangular transducer elements.
It is an object of the present invention to provide a suitable package for housing a generally rectangular, in plan view, fluid pressure sensing capacitive transducer. Yet another object is the provision of a housing for receiving rectangular-shaped (in plan view) transducer elements which has essentially the same outer shape and dimensions as housings used for receiving cylindrical fluid pressure sensing capacitive transducers already in the market place so that the packages can be interchanged in a common application. Yet another object of the invention is the provision of a package having a cylindrical port fitting for interfacing with a fluid pressure source whose pressure is to be monitored having a rectangular-shaped (in plan view) sensing element mounted therein in which a circular sealing element is reliably received between the port fitting and the sensing element. Yet another object of the invention is the provision of connector means for electrically interconnecting a generally thin, rectangular (in plan view) sensing element to an electrical circuit mounted in the package and for providing a suitable interconnection between a ground conductor of the electrical circuit and the port fitting.
Briefly, in accordance with the invention, a base assembly has a first base member formed of electrically insulating material mounting a plurality of elongated terminal members in spaced apart, parallel relationship with an end of the terminal members received in an electronics chamber formed at one end of the first base member. A flexible circuit bent generally in a U-shaped configuration with one lobe portion overlying a second lobe portion is received in the chamber for attachment of terminal pads of the circuit on one, the first, lobe portion with the terminal members. A ground portion extends from the flexible circuit out of the chamber through a slot formed in the first base member. A pressure sensing capacitive transducer element has a rectangular configuration in plan view and is composed of a substrate having a diaphragm thereon with the contact pads on an outer surface along an edge of the element. The transducer element is butted up against an upstanding lip extending from the outer end of the other, the second, lobe portion of the flexible circuit. Generally U-shaped edge connectors are received over the edge of the transducer element and outer end of the second lobe portion to electrically join the contact pads and electrical circuitry of the flexible circuit.
A cover, or second base member, is receivable over the top of the base member and is formed with a wall having a circular fluid pressure receiving opening and with a first sealing gasket seat and a second sensing element seat coaxially formed in the wall with the circular opening. A generally circular, annular sealing gasket is received in the circular opening of the cover and is provided with outwardly extending tabs received on the first gasket seat and the sensing element is received in the second sensing element seat. The cover is provided with opposing leg members having an outer lip which are received in slots formed in the first base member and snap into transversely extending openings or notches to attach the cover to the first base member with the corner portions of the rectangular transducer element received on the end face of the first base member. A port fitting of suitable material, such as aluminum, is then received over the cover and is clamped to a circumferential flange of the first base member and with the ground portion of the flexible circuit pressed against the port fitting.